Introduce `asdf.util.load_yaml` #2389

Job	Run time
astropy / Load tox environments	4s
third-party / Load tox environments	7s
stsci / Load tox environments	9s
asdf / Load tox environments	6s
astropy / asdf-astropy (ubuntu-latest)	2m 31s
astropy / specutils (ubuntu-latest)	1m 32s
asdf / asdf-wcs-schemas (ubuntu-latest)	1m 14s
asdf / asdf-coordinates-schemas (ubuntu-latest)	2m 3s
third-party / weldx (ubuntu-latest)	2m 28s
third-party / sunpy (ubuntu-latest)	2m 9s
third-party / dkist (ubuntu-latest)	2m 54s
stsci / gwcs (ubuntu-latest)	1m 4s
stsci / jwst (ubuntu-latest)	8m 10s
stsci / stdatamodels (ubuntu-latest)	2m 17s
stsci / stpipe (ubuntu-latest)	35s
stsci / roman_datamodels (ubuntu-latest)	1m 23s
	28m 46s

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